Method of forming a sheet metal fin strip element for heat exchange structures



Jan. 26, 1965 A B MODINE 3,167,046

METHOD OF FORMING A SHEET METAL FIN STRIP ELEMENT FOR HEAT EXCHANGE STRUCTURES Original Filed Jan. 24, 1956 @15 [T15 Z O 0 OPEN t E D (O) l f 7206712 07 14 3 I ari/Lurzfiffaac'ne O PEN/RN U] United States Patent 3 167,046 lVHETHfiD 8F FGRMiNG A SHEET METAL FIN STRiP ELEMENT FUR HEAT EXHAYGE STRUCTURES Arthur B. Medina, Racine, Wis., assignor to Mini R113 Manufacturing Company, Racine, Wis, a corporation of Wisconsin Griginai application Jan. 24, 1956, Ser. No. 560,997, new Patent No. 2,965,357, dated Dec. 20, 1960. Divided and this appiicatio'n Nov. 16, 196i Ser. No. 69,697 4 (Ilaims. (Ql. 113 118) The invention relates generally to a heat exchange structure and more. particularly to a secondary heat transfer surface therefor, and a method of making the same, and is a division of my co-pending application Serial No. 560,997 filed January 24, 1956, now United States Patent No. 2,965,357, dated December 20, 1960.

V The invention has among its objects the method of forming a heat exchange surface in the form of a sheet metal fin strip element to provide a secondary heat transfer surface having a high ratio of surface area to weight, whereby a more efhcient distribution of the metal is achieved and improved results are obtained over other structures utilizing the same amount of metal.

Another object of the invention is the method of forming a sheet metal fin strip element for a heat exchange structure wherein the fin strip element, while having very thin portions, is provided with a relatively high degree of rigidity or stiffness whereby it may be handled and assembled into a core structure with substantially normal manufacturing techniques.

Another object of the invention is the method of forming a sheet metal fin strip element for a heat exchange structure having the above advantages in which some of the material used for extended surface and for increasing the rigidity of the heat exchange structure may also be employed as means for spacing one fin member from the other and if desired, providing turbulence of air flow.

A further object of the invention is the production of a sheet metal heat transfer fin strip element by a novel method whereby some of the metal which normally would be formed into tube-engaging flanges, or the like, may be utilized as a part of the heat transfer surface.

A further object of the invention is the development of a novel method of fabricating a sheet metal heat transfer fin strip element or the like having the above advantages wherein the distribution of metal and an increase in surface area maybe accomplished in a plurality of steps, one of which includes the more or less uniform stretching of the metal prior to forming operations and another which includes the stretching and forming of the material at desired points during the forming operation.

Many other objects and advantages of the method of forming a sheet metal fin strip element for heat exchangers herein shown and described will be obvious to those skilled in the art from the disclosure herein given.

To this end my invention comprises the novel method of forming a sheet metal fin strip element for the construction, arrangement and combination of parts for heat exchange structures herein shown and described, and more particularly pointed out in the claims.

In the drawings, wherein like reference characters inclicate like or corresponding parts:

FIG. 1 is a perspective view of a portion of a heat exchange structure embodying the present invention;

FIGv 2 is a top plan view of portions of a fin element during the forming thereof illustrating how successive operations may be performed in carrying out the invention;

FIG. 3 diagrammatically illustrates one Way in which initial stretching of the material may be accomplished;

, 3,lfi?,fi iti Patented Jan. 26, 1965 FIG. 4 diagrammatically illustrates successive steps which also may be utilized in the initial stretching of the material;

FIG. 5 is a top plan view of a portion of a modified fin element embodying the invention; and

FIG. 6 is an end elevational view of a plurality of stacked elements such as that illustrated in FIG. 5.

The present invention contemplates the formation of heat transfer elements from sheet metal comparable to that presently employed for such operations, and by utilization of the present invention results in such an element having increased surface area, better distribution of metal, and a higher etficiency than elements heretofore made from like material.

Referring to the drawings, FIG. 1 illustrates the embodiment of the invention in a secondary surface fin structure adapted to be associated with a plurality of fluid conducting tubes 1, the fin structure comprising a plurality of fin elements 2 having slots 3 therein, and of a size to receive respective tubes 1. While the particular construction illustrated discloses the tubes as being in sertable from the longitudinal or side edges of the strips 2, the means for receiving the prime surface elements of the heat exchange structure may besuitably formed in any desired manner, as for example, in the form of apertures whereby the fin element completely encircles each tube.

In the embodiment of the invention illustrated in FIG. 1, each fin strip 2 is provided along its opposite longitudinal edges with longitudinally spaced recesses 3 adapted to receive the tubes 1 and positioned between the slots 3 along one edge of the fin strip and the slots along the opposite edge of the fin strip are a series of longitudinally extending continuous corrugations 4, the latter being illustrated as disposed more or less uniformly on opposite sides of the faces of each strip. Positioned between corresponding pairs of slots 3 along the same side edge of the strip is a plurality of transversely extending deformations or corrugations 5 and 5, so arranged that every other intermediate portion between the slots 3 is provided with a pair of corrugations 5, while each alternate portion is provided with a single corrugation 5'. As illustrated in FIG. 1 and more clearly shown in FIG. 2, theslots 3 along one edge of the strip may be transversely aligned with the corresponding slots along the opposite edge of the strip, with the corrugations intermediate adjoining tubes being reversed along opposite edges of the strip, whereby a portion between a pair of tube-receiving slots is provided with two corrugations 5, while the corresponding portion along the opposite edge of the strip is provided with a single corrugation 5. Thus by reversing alternate strips, end forend, as illustrated in FIG. 1, the corrugations 5 and 5' may be staggered to form effective means for properly spacing the fin strips along the tubes 1 and eliminate a necessity of providing unnecessarily long flanges along the tubes 1 for the purpose of spacing the strips as is common practice in structures of this type.

In actual practice, the thickness of the stock from which the fins 2 may be formed is normally very thin and varies from a foil-like thickness of only several thousandths to seven or eight thousandths or more. Flat strips of material on the order of this thickness are quite flexible and easily bent or distorted. Likewise, the assembly of such flexible strips in a core structure would be extremely difiicult. However, by utilizing means such as the corrugations 4 and 5, extremely thin strips may be employed, at the same time having a satisfactory degree of rigidity or stiffness to enable the use of substantially normal manufacturing techniques.

FIG. 2 illustrates the formation of a fin structure of the type illustrated in FIG. 1 from a blank strip to the finished fin element, and while the forming of the strip is illustrated in a series of individual steps, two or more of such steps may be simultaneously performed as will hereinafter be discussed in detail. In the sequence illustrated in FIG. 2, theblank strip B may be initially provided with longitudinally extending corrugations 4, following which the transverse corrugations 5 and 5 may be produced. The last section of strip material illustrated in FIG. 2 discloses the finished strip with the slots 3 formed therein, with the arrangement being such that opposite portions of the strip are provided with corrugations 5 and 5.

The corrugations 4, 5 and 5' are produced by stretching the metal forming the same and should not be confused with the usual type of corrugated structure wherein the corrugations are formed with substantially little stretching of the material comprising the same, the overall dimensions of the material being correspondingly reduced as the corrugations are made. However, it will be apparent that in the construction illustrated in FIG. 2, the width and length of the strip remains substantially constant prior and subsequent to the formations of the particular corrugations. Consequently, the thickness of the material forming the corrugations will be less than the thickness of the material of uncorrugated portions of the strip. In forming a structure such as that illustrated in FIG. 2, I normally prefer to form the slots 3 or other equivalent means simultaneously with the formation of the corrugations 5 and 5, whereby a portion of the metal that would normally comprise the flanges 6 may be drawn into the intermediate portion of the fin strip, eliminating unnecessary thickness of the flanges and resulting in more effective use of the material.

While in some cases it may be possible to reduce the thickness of the material during the forming operations in connection with the corrugations 4, 5 and 5, for most cases I prefer to accomplish a portion of the reduction prior to the forming operation, and FIGS. 3 and 4 illustrate means for accomplishing a substantially uniform stretching of the material prior to the forming operations.

FIG. 3 illustrates two pairs of rollers 7 and 7 and 8 and 8', each pair of rollers being operatively connected by respective pairs of gears 9 and 9' and I1 and 11. Assuming the lower rolls 7 and 8 are rotated in a clockwise direction and the rolls 7' and 8 in a counterclockwise direction, sheet material B will be advanced in the direction of the arrow or to the right as viewed in FIG.

' 3, so that the rolls 7 and 7' may be considered the leading rolls and 8 and 8' trailing or succeeding rolls. The driving rolls 7 and 8 may be operatively connected by suitable means, as for example, a chain 12 indicated diagrammatically in FIG. 3. In the embodiment illustrated in FIG. 3, the rolls 7 and 7' have a periphery of approximately ten percent greater than the periphery of the rolls 8 and 8, and if both pairs of rolls are driven at the same speed, the leading rolls 7 and 7' will advance the blank B at a greater rate than the rolls 8-3, resulting in a stretching of the material substantially proportional to the difference in size of the rolls. To insure adequate traction on the material passing through the rolls, one roll of each pair may be knurled or otherwise suitably shaped, while the cooperable roll may be relatively resilient, as for example, provided with a face of rubber or the like. In this type of operation, strip material in coils may be fed into the stretching mechanism and subsequently coiled or fed directly into the forming mechanism. Rolls of equal diameter could also be employed, in which case the leading rolls would be rotated at a sufficiently greater speed to provide the desired results.

FIG. 4 illustrates an intermittently operated stretching mechanism adapted to form the stretched metal into blanks of predetermined length. In this construction the material may be initially fed by a pair of rollers 13 and 14 adapted to feed the material B through a pair of cooperable clamping jaws l5 and 16, one of which may be provided with a shearing blade 17. The clamping jaws 15 and 16 may be actuated by suitable mechanism for longitudinal movement toward or away from the rolls 13 and 14, whereby following closing of the jaws 15 and 16 as illustrated in FIG. 4B, following feeding of the strip, the members 15 and 16 may be moved away from the rollers 13 and 14-, the latter being suitably held in stationary relationship during such movement, as illustrated in FIG. 4C, thus stretching the material extending between rollers 13 and 14 and the jaws 15 and 15. The jaws l5 and 16 may then be opened as illustrated in FIG. 4D, following which they may be returned to their original position as illustrated in FIG. 4E and the material B advanced as indicated in FIG. 4A, and the cycle then repeated. Several of the steps illustrated in FIG. 4 may be combined as for example, returning of the jaws 15 and 16 and feeding of the strip material. After one sequence of operation has been performed, on the closing of the jaws during the next cycle the stretched portion of the strip will be severed by the shearing member 17 to form a stretched blank of predetermined length.

FIGS. 5 and 6 illustrate a modified arrangement or corrugations in conjunction with a staggered tube arrangement. In this construction, as illustrated in FIG. 5, the tube-receiving slots 3' adjacent one longitudinal edge of the strip are longitudinally offset or staggered with respect to the corresponding slots along the opposite longitudinal edge, and extending between each adjacent pair of slots is a pair of transversely extending corrugations 5", the corrugations in this construction being aligned on the as sembled fins, whereby such corrugations are not employed as spacing means.

By means of the present invention, the thickness of the fin material may be reduced, resulting in a more efficient use of the material therein, and increased efiiciency in the heat exchange structure. Likewise, while lighter materials may be employed, suitable rigidity and stiffness in the fin element is achieved to enable normal handling and assembly techniques.

As previously pointed out, it will be noted that the corrugations, both transversely and longitudinally, are formed from metal that has been stretched to provide the increased area required without a corresponding decrease or shortening of the blank which would normally occur in the fabrication of the usual type of corrugated structure. In other words, the overall dimensions of a length of fin structure produced in accordance with the present invention, as Well as the width, will remain substantially constant from the initiation of the forming operations to the completion thereof.

Having thus described my invention, it is obvious that various immaterial modifications may be made in the same without departing from the spirit of my invention; hence, I do not wish to be understood as limiting myself to the exact form, construction, arrangement and combination of parts herein shown and described or uses mentioned.

What I claim as new and desire to secure by Letters Patent is:

1. The method of forming a sheet metal fin strip element for heat exchange structures from a sheet metal strip of substantially foil-like thickness, which comprises the steps: stretching the metal strip to substantially uniformly reduce the thickness and increase the area thereof, forming the longitudinally extending intermediate portion of the sheet metal strip out of the normal plane of the latter to increase the area in a transverse direction and to decrease the thickness of such portion, deforming the longitudinal portions on opposite sides of said intermediate portions at predetermined spaced points out of the plane of said sheet metal strip to increase the area in a longitudinal direction and to decrease the thickness of the metal at such points, and forming the sheet metal strip intermediate said longitudinally spaced points for engagement with elements of such a heat exchange structure so that the decreased thickness of the deformed longitudinal portions of the sheet metal fin strip element between said spaced points for engagement with elements of said heat exchange structure provides in addition to stiffening action, tapered fin portions whereby the heat ex change surface of said fin strip element has a high ratio of surface area to weight.

2. The method of forming a sheet metal fin strip element for heat exchange structures from a sheet metal strip of substantially foil-like thickness, which comprises the steps: stretching the sheet metal strip to substantially uniformly reduce the thickness and increase the area thereof, deforming the longitudinally extending intermediate portion of the sheet metal strip out of the normal plane of the latter providing longitudinally extending V-shaped corrugations to impart a longitudinal stiffening of said fin strip element and to increase the area in a transverse direction and to decrease the thickness of such portion, while maintaining the overall transverse dimension of the sheet metal strip substantially constant, deforming the longitudinal portions on opposite sides of said intermediate portions at predetermined spaced points out of the plane of said sheet metal strip to increase the area in a longitudinal direction and to decrease the thickness of the metal at such points to provide transversely extending V-shaped corrugations terminating at their inner ends adjacent the longitudinally extending V-shaped corrugations operative to impart a transverse stiffening of the respective portions of the fin strip element intermediate the longitudinal edges of the sheet metal strip and the longitudinally extending V-shaped corrugations therein, the material of said longitudinally and transversely extending corrugations being provided from the distribution of material of uniform thickness of said fin strip element, while maintaining the overall longitudinal dimension of the sheet metal strip substantially constant, forming the sheet metal strip intermediate said longitudinally spaced points for engagement with elements of such a heat exchange structure, and said transversely extending V- shaped corrugations formed to provide two V-shaped corrugations between certain pairs of tubular elements of such a heat exchanger and one V-shaped corrugation between other tubular elements, whereby upon reversal of alternate fin strips in forming the heat exchanger, each transverse V-shaped corrugation is disposed out of vertical alignment with the corresponding V-shaped corrugations of the adjacent fin strips.

3. The method of forming a sheet metal fin strip element for heat exchange structures from a sheet metal strip of substantially foil-like thickness which comprises the steps: stretching the sheet metal strip to substantially uniformly reduce the thickness and increase the area thereof, deforming he longitudinally extending intermediate portion of the sheet metal strip out of the normal plane of the latter providing longitudinally extending V-shaped corrugations to impart a longitudinal stiffening of said fin strip element and to increase the area in a transverse direction and to decrease the thickness of such portion while maintaining the overall transverse dimension of the sheet metal strip substantially constant, deforming the longitudinal portions on opposite sides of said intermediate portions at predetermined spaced points out of the plane of said strip to increase the area in a longitudinal direction and to decrease the thickness of the metal at such points to provide transversely extending V-shaped corrugations terminating at the inner ends adjacent the longitudinally extending V-shaped corrugations operative to impart a transverse stiifening of the respective portions of the fin strip element intermediate the longitudinal edges of the sheet metal strip and the longitudinally extending V-shaped corrugation therein, the material of said longitudinally and transversely extending corrugations being provided from the distribution of material of uniform thickness of said fin strip element, while maintaining the overall longitudinal dimension of the sheet metal strip substantially constant, and simultaneously forming the sheet metal strip intermediate said longitudinally spaced points for engagement with elements of such a heat exchange structure, whereby a portion of the metal originally at the engageable area is drawn into the sheet between the latter.

4. The method of forming a secondary surface sheet metal fin member for a heat exchange structure, from sheet metal of substantially foil-like thickness, which comprises the steps: stretching a piece of sheet metal of substantially foil-like thickness to substantially uniformly reduce the thickness and increase the area thereof, and further reducing the thickness thereof at predetermined points by forming transverse corrugations whereby said sheet metal of substantially foil-like thickness varies in thickness in a predetermined pattern from that initially stretched to that of the subsequently stretched portions so that the thinned portions of said fin member between said transverse corrugations provide in effect, in addition to said stiffening action, tapered fin portions whereby the heat transfer surface of said fin member has a high ratio of surface area to Weight.

References Cited in the file of this patent UNITED STATES PATENTS 2,046,791 Przyborowski July 7, 1936 2,306,792 Moore Dec. 29, 1942 2,834,583 Oldberg et a1. May 13, 1958 2,983,483 Modine May 9, 1961 FOREIGN PATENTS 160,046 Australia Nov. 19, 1953 667,327 Germany Nov. 9, 1938 466,539 Great Britain May 31, 1937 512,230 Great Britain -0 Aug. 30, 1939 

1. THE METHOD OF FORMING A SHEET METAL FIN STRIP ELEMENT FOR HEAT EXCHANGE STRUCTURES FROM A SHEET METAL STRIP OF SUBSTANTIALLY FOIL-LIKE THICKNESS, WHICH COMPRISES THE STEPS: STRETCHING THE METAL STRIP TO SUBSTANTIALLY UNIFORMLY REDUCE THE THICKNESS AND INCREASE THE AREA THEREOF, FORMING THE LONGITUDINALLY EXTENDING INTERMEDIATE PORTION OF THE SHEET METAL STRIP OUT OF THE NORMAL PLANE OF THE LATTER TO INCREASE THE AREA IN A TRANSVERSE DIRECTION AND TO DECREASE THE THICKNESS OF SUCH PORTION, DEFORMING THE LONGITUDINAL PORTIONS ON OPPOSITE SIDES OF SAID INTERMEDIATE PORTIONS AT PREDETERMINED SPACED POINTS OUT OF THE PLANE OF SAID SHEET METAL STRIP TO INCREASE THE AREA IN A LONGITUDINAL DIRECTION AND TO DECREASE THE THICKNESS OF THE METAL AT SUCH POINTS, AND FORMING THE SHEET METAL STRIP INTERMEDIATE SAID LONGITUDINALLY SPACED POINTS FOR ENGAGEMENT WITH ELEMENTS OF SUCH A HEAT EXCHANGE STRUCTURE SO THAT THE DECREASED THICKNESS OF THE DEFORMED LONGITUDINAL PORTIONS OF THE SHEET METAL FIN STRIP ELEMENT BETWEEN SAID SPACED POINTS FOR ENGAGEMENT WITH ELEMENTS OF SAID HEAT EXCHANGE STRUCTURE PROVIDES IN ADDITION TO STIFFENING ACTION, TAPERED FIN PORTIONS WHEREBY THE HEAT EXCHANGE SURFACE OF SAID FIN STRIP ELEMENT HAS A HIGH RATIO OF SURFACE AREA TO WEIGHT. 